Chronic metabolic acidosis, a relatively common clinical disorder found in the patients with renal insufficiency and renal tubular acidosis, cause dissolution of bone mineral. This research has the long-term objective of improving our understanding of how protons cause bone mineral dissolution. This will be accomplished by studying acid induced calcium release from cultured mouse calvariae using a high resolution scanning ion microprobe and x-ray diffraction in conjunction with measurements of medium saturation and ion flux. Neonatal mouse calvaria (frontal and parietal bones of the skull) in culture is an appropriate model in which to study the effects of protons on bone since calvariae release calcium an buffer protons during culture in acidic medium, as human bone dose in vivo. We will attempt to attain a better understanding of how changes in pH effect the bone mineral in order to construct a model of proton induced bone mineral dissolution. We propose to test the following hypothesis: 1) That chronic culture of bone in an acidic medium results in similar changes in one surface elements as chronic metabolic acidosis in vivo. We will determine the change in surface elements, using the ion microprobe, of cultured neonatal mouse calvariae in response to a chronic (24-96 hrs) lowering of medium bicarbonate concentration, an in vitro model of chronic metabolic acidosis. We will determine the change in mineral composition in neonatal mice injected with NH4C1, an in vivo model of chronic metabolic acidosis, and compare them to calvariae cultured in acidic medium. 2) That pH induced alterations in bone cell function are instrumental in augmenting calcium release during chronic culture in an acidic medium. This will be tested by treating the calvariae with agents which alter bone cell function, but do not directly affect the bone mineral, and comparing rates of proton induced calcium efflux, differences in the mineral surface elements and differences in the mineral phases. 3) That calcium carbonate is the initial phase of the bone mineral depleted during chronic culture in an acid medium by determining the phase(s) of mineral depleted in chronic culture using x-ray diffraction. 4) That hormonally induced bone resorption has the same effect on the bone mineral surface elements and mineral phases as proton induced bone resorption. This will be tested by culturing calvariae with parathyroid hormone and comparing them to calvariae cultured in and acidic medium. 5) That an elevated partial pressure of carbon dioxide (pC02) will increase bone carbonate content by culturing calvariae in an elevated pC02, a model of chronic respiratory acidosis, and determining the mineral phases by x-ray diffraction.